Modern motor vehicles include a large number of electrical devices and electrical units and the number of such electrical devices and units still increases, since buyers of motor vehicle demand these electrical devices and units often in a built-in fashion to provide convenience to the driver of the motor vehicle.
The electrical devices and units built-in a motor vehicle all have to be energized by the power supply of the motor vehicle, typically a battery of limited capacity. The battery of a motor vehicle is charged during operation of the engine of the motor vehicle so that the power consumption of electrical devices and units of the motor vehicle represents no serious problem while the engine is running. But the power consumption of electrical devices and units consuming power from the battery when the engine of the motor vehicle is not running causes a decharging of the battery and hence causes a problem. Especially, electrical devices and units operable in a stand-by operation mode have to be designed in a power saving way. The stand-by operation mode allows for example to activate the device or unit being in the stand-by operation mode via a central control unit of the motor vehicle.
A motor vehicle built-in unit for mobile communication devices is used to couple a mobile communication device such as a mobile phone, a communication handheld and the like, to the further electrical devices and units included in the motor vehicle. The motor vehicle built-in unit allows to couple to an external speaker, e.g. of a car radio, an external microphone, e.g. implemented in the dashboard, to an antenna e.g. having a power amplifier, a remote control e.g. having keys for operating functions of the mobile phone, to the electric circuits of the motor vehicle e.g. via a data communication bus of the motor vehicle for remote operating and the like. Typically such a motor vehicle built-in unit for mobile communication devices is operable with stand-by operation mode to be energizable within different situations.
The manufacturer of motor vehicles impose strict regulations for the requirements to be fulfilled by electrical devices and units to be included in motor vehicles, especially power consumption of electrical devices and units being in a stand-by operation mode is of special interest. The power consumption has to be minimized or has to be below a maximum level or power consumption, in order to ensure that the battery is not drained too much, especially in case the motor vehicle is parked. Certain electrical circuits have been implemented into such devices and units to offer stand-by operation mode. These electrical circuits of the state of the art comprise a large number of active components conventionally requiring to be energized by a voltage regulator.